Clock of the Long Now

As of June 2018[update], two more prototypes are on display at The Long Now Museum & Store at Fort Mason Center in San Francisco.

In the words of Stewart Brand, a founding board member of the foundation, "Such a clock, if sufficiently impressive and well-engineered, would embody deep time for people.

Many options were considered for the power source of the clock, but most were rejected due to their inability to meet the requirements.

In the current design, a slow mechanical oscillator, based on a torsional pendulum, keeps time inaccurately, but reliably.

At noon, the light from the Sun, a timer that is accurate but (due to weather) unreliable, is concentrated on a segment of metal through a lens.

However, every human culture counts days, months (in some form), and years, all of which are based on lunar and solar cycles.

(For instance, for a short period of time the count of 29.5 days per lunar month may suffice, but over 10,000 years the number 29.5305882 is a much more accurate choice.)

For instance, the ratio of day to years depends on Earth's rotation, which is slowing at a noticeable but not very predictable rate.

The digital scheme allows that conversion ratio to be adjusted, without stopping the clock, if the length of the day changes in an unexpected way.

The Long Now Foundation has purchased the top of Mount Washington near Ely, Nevada,[8] which is surrounded by Great Basin National Park, for the permanent storage of the full-sized clock, once it is constructed.

It will be housed in a series of rooms (the slowest mechanisms visible first) in the white limestone cliffs, approximately 10,000 feet (3,000 m) up the Snake Range.

Hillis chose this area of Nevada in part because it is home to a number of dwarf bristlecone pines, which the Foundation notes are nearly 5,000 years old.

Neal Stephenson's 2008 novel Anathem was partly inspired by his involvement with the project, to which he contributed three pages of sketches and notes.